Certainly sounds like a Herc. And the 'contrails' could be, as already mentioned, just vapour due to altitude/humidity. Or perhaps even fuel dumping?
I know when I've seen RAF Hercs at low level, say on approach, or para-dropping, the exhaust trails, mixing with condensation vapour from the wing tanks or flaps, due I presume to pressure generation because of angle of attack, can often make it look like 3 trails per wing.